This invention relates to Pressure Swing Adsorption (P.S.A.) or Rapid Pressure Swing Adsorption (R.P.S.A.) processes and, more particularly, to a new valve system to control gas flow for R.P.S.A. and P.S.A. systems.
The R.P.S.A. process and the P.S.A. process provide means for producing an oxygen-enriched gas that can be used at high altitude or as a breathing atmosphere by persons suffering from respiratory ailments. Both R.P.S.A. and P.S.A. processes utilize a feed gas mixture that is fed into an adsorbent bed that adsorbs the different gas components to differing degrees so that the more readily adsorbable component is retained in the adsorbant bed. Typically, the feed gas is air and nitrogen is the more readily adsorbable component that is adsorbed out, leaving an oxygen-enriched gas affluent. Examples of prior art which disclose various multiple bed, rapid pressure swing adsorption systems for gases include U.S. Pat. Nos. 4,194,891; and 4,194,892; and 4,406,675.
The cyclic process of a typical R.P.S.A. system includes:
(1) feeding the gas mixture to the feed or intake end of the bed for selective adsorption of the more readily adsorbable gas component with withdrawal of the less readily adsorbable component as a product effluent from the opposite or discharge end of the bed,
(2) countercurrently depressurizing the bed, with the more readily adsorbable gas component thereby being exhausted through the feed end of the bed, and
(3) repressurizing the bed from the lower pressure reached during countercurrent depressurization to a higher intermediate pressure or to the high final adsorption pressure for the adsorption of the more readily adsorbable component from additional quantities of the feed gas mixture during the next processing cycle in the bed.
A pair of valves is required to cycle the gas mixture into and out of a one-adsorber bed system. Because of the intermittent flow of fluid with only one bed, typical systems utilize two adsorber beds and a set of four valves. These systems typically utilize solenoid actuated, four-way, three-way, or two-way pneumatic valves. A controlled timer or other electronic device is required to control the timing cycle. The most commonly used valve is the sliding spool, four-way valve that is solenoid actuated as commonly used in industrial applications.
However, the solenoid actuated sliding spool type valves are prone to stick in position. In addition, these valves are expensive to operate since they require some system pressure to move the spool and require the significant additional cost of providing an electrical controller for the timing. Solenoid valves also produce a loud popping sound when actuated. This must be muffled or attenuated in medical and industrial applications.
An object of the present invention is to provide a valve system for the operation of R.S.P.A. and P.S.A. systems.
A further object of the invention is to provide such a valve system that is more reliable than those presently available; can be operated at a lower cost; is less costly to construct; and that operates with a significantly lower noise level than valves presently available.